Conventional blood viscosity measurement devices deform blood between two controlled surfaces or, alternatively, let blood move from a human body to a flow restrictor tube and measure flow characteristics such as the flow resistance during the blood movement in the tube, in order to measure the viscosity of the blood or the aggregation ratio of blood cells.
PCT Published Patent Application No. WO01/036936 discloses a dual riser/single capillary viscometer. The viscometer monitors the change in height of two, oppositely-moving, columns of blood from the circulating blood of a patient and, given the dimensions of a capillary tube through which the blood flows, determines the blood viscosity over a range of shears, especially low shears. The system includes a tube set (disposable or non-disposable) that includes a pair of riser tubes, a capillary tube of predetermined dimensions that is coupled between the riser tubes (or that forms a portion of one riser tube) and a valve mechanism for controlling the circulating flow of blood from the patient into the riser tubes. Respective sensors monitor the movement of the columns of blood in each of the riser tubes and an associated microprocessor analyzes these movements, along with the predetermined dimensions of the capillary tube, to determine the viscosity of the patient's circulating blood.
To supply a blood sample to measure viscosity, a viscometer may obtain blood directly from a needle or tube connected to a vein or indirectly from a reservoir containing blood. Conventional reservoirs are evacuated tubes (or “Vacutainers”), such that they can supply blood by applying a predetermined pressure of air or other gas into the reservoirs. FIG. 1 is a front view illustrating one example of a conventional blood transferring device using air. The conventional blood transferring device of FIG. 1, which supplies blood manually, comprises a reservoir 20 including a silicone packing 25 on its top, a blood needle 30 passing through the silicone packing 25 and reaching the blood of the reservoir 20, an air needle 40 passing through the silicone packing 25, the end of which is located above the fluid level of the blood, and a syringe 50 for supplying air into the reservoir 20 via the air needle 40.
As an operator slowly introduces air into the reservoir using the syringe 50, the air injected via the air needle 40 produces a relatively higher pressure on the fluid level of the blood, and subsequently the higher pressure in the reservoir pushes the blood to the blood viscometer 60 through the blood needle 30. However, when the operator operates the syringe 50 manually, it is practically impossible to transfer the blood under a contant pressure and flow because it is very difficult to maintain a constant injection rate of air to the vaccum reservoir. Moreover, since the air needle 40 and the blood needle 30 are installed independently and controlled to different heights relative to the fluid level of the blood, it is difficult to precisely position both needles at the desired locations within the reservoir.
Additionally, because the two needles 30, 40 are physically separated, it is substantially difficult to automate the blood delivery system for the viscosity measurement of blood. For example, when introducing two needles 30, 40 through the silicone packing, the needles may be bent or curved. Moreover, when the needles 30 and 40 are removed from the rubber packing 25 at the end of a blood viscosity measurement, the needles may not be smoothly pulled out or may suddenly spring out. Accordingly, even with special precautions, an operator can be injured by a removed needle contaminated by a patient's blood, as well as be exposed to the risk of being infected by blood-borne diseases.